Rivet analyses

title: BABAR_2012_I1079912

Lepton momentum spectrum in $B\to X_u\ell\nu$ decays

Experiment: BABAR (PEP-II)

Inspire ID: 1079912

Status: VALIDATED NOHEPDATA

Authors: - Peter Richardson

References: - Phys.Rev.D 86 (2012) 032004

Beams: * *

Beam energies: ANY

Run details: - Any process producing B+, B0 mesons, originally Upsilon(4S) decay

Measurement of the branching ratio for $B\bar{X}\to X_u \ell\bar\nu_\ell$ for different lower cuts on the lepton momentum.

Source code:BABAR_2012_I1079912.cc

```c++ // -- C++ --

include "Rivet/Analysis.hh"

include "Rivet/Projections/UnstableParticles.hh"

namespace Rivet {

/// @brief B -> X_u ell nu class BABAR_2012_I1079912 : public Analysis { public:

/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(BABAR_2012_I1079912);


/// @name Analysis methods
/// @{

/// Book histograms and initialise projections before the run
void init() {
  // projections
  declare(UnstableParticles(Cuts::abspid == 511 or Cuts::abspid == 521), "UFS");
  // histograms
  book(_h, 1, 1, 1);
  book(_nB, "/TMP/nB");
}

void findDecayProducts(Particle parent,
                       Particles& em,
                       Particles& ep,
                       Particles& nue,
                       Particles& nueBar,
                       bool& charm) {
  for (const Particle& p : parent.children()) {
    if (PID::isCharmHadron(p.pid())) {
      charm = true;
    }
    else if (p.pid() == PID::EMINUS) {
      em.push_back(p);
    }
    else if (p.pid() == PID::EPLUS) {
      ep.push_back(p);
    }
    else if (p.pid() == PID::NU_E || p.pid() == PID::NU_MU) {
      nue.push_back(p);
    }
    else if (p.pid() == PID::NU_EBAR || p.pid() == PID::NU_MUBAR) {
      nueBar.push_back(p);
    }
    else if (PID::isBottomHadron(p.pid())) {
      findDecayProducts(p, em, ep, nue, nueBar, charm);
    }
    else if (!PID::isHadron(p.pid())) {
      findDecayProducts(p, em, ep, nue, nueBar, charm);
    }
  }
}

/// Perform the per-event analysis
void analyze(const Event& event) {
  if (_edges.empty()) _edges = _h->xEdges();
  const UnstableParticles& ufs = apply<UnstableParticles>(event, "UFS");
  for (const Particle& p : ufs.particles()) {
    if (p.children().empty()) continue;
    if (p.children()[0].abspid() == p.abspid()) continue;
    _nB->fill();
    bool charm = false;
    Particles em, ep, nue, nueBar;
    findDecayProducts(p, em, ep, nue, nueBar, charm);
    if (charm) continue;
    FourMomentum pl, pnu;
    if (em.size() == 1 && nueBar.size() == 1) {
      pl = em[0].momentum();
    }
    else if (ep.size() == 1 && nue.size() == 1) {
      pl = ep[0].momentum();
    }
    else
      continue;
    LorentzTransform boost = LorentzTransform::mkFrameTransformFromBeta(p.momentum().betaVec());
    pl = boost.transform(pl);
    double pp = pl.p3().mod();
    double Emin = 1.0;
    for (unsigned int ix = 0; ix < _edges.size(); ++ix) {
      if (pp > Emin) _h->fill(_edges[ix]);
      Emin += 0.1;
    }
  }
}


/// Normalise histograms etc., after the run
void finalize() {
  // 1e3 due br normalization and 0.1 to remove bin width
  scale(_h, 1e3 / *_nB);
}

/// @}


/// @name Histograms
/// @{
BinnedHistoPtr<string> _h;
CounterPtr _nB;
vector<string> _edges;
/// @}

};

RIVET_DECLARE_PLUGIN(BABAR_2012_I1079912);

} ```